Electric valve circuits



Nov. 26, 1940. M. M. MORACK ELECTRIC VALVE CIRCUITS Filed May 26, 1938 Fig.5.

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Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE ELECTRIC VALVE CIRCUITS New York Application May 26, 1938, Serial No. 210,224

4 Claims.

My invention relates to electric valve circuits and more particularly to control systems for electric valve apparatus of the type employing ionizable mediums and in which the control of the conductivity of the electric valve apparatus is efiected by means of magnetic fields.

In electric valve circuits, particularly in electric valve circuits of the type commonly called parallel inverters, there has been evidenced a decided need for improved control systems embodying features which afford protection for the oathodes of the electric valves employed and which are not adversely affected by transient voltages and variations in the characteristics of the valves. A decided commercial field exists for inverters that can be made to operate with freedom from commutation failure. Where the electric valve inverters have been employed using electric valves of the grid-controlled type, it has been important to provide expensive and rather complicated grid circuits which include current limiting resistances, specially designed transformers and biasing means. It is frequently desirable to provide inverter circuits which employ a minimum number of control elements and which are susceptible of precise and reliable operation.

Although the principle of magnetically controlling the initiation of arc discharges in electric valve means which use ionizable mediums has been well-known and appreciated, the prior art arrangements have not used this principle in arrangements readily adaptable for comercial application. There is a need for improved control circuits for electric valves of the magnetically controlled type which will permit the general application of this type of valve to translating circuits which are subjected to varied load conditions and which are rugged in construction and reliable in operation. I

It is an object of my invention to provide new and improved electric valve circuits.

It is another object of my invention to provide new and improved control systems for electric valves.

It is a further object of my invention to provide new and improved control circuits for electric valve apparatus of the type employing ionizable mediums and in which the conductivity of the electric valve apparatus is controlled by magnetic fields.

In accordance with one of the illustrated embodiments of my invention, I provide an improved electric valve translating circuit for transmitting energy from a direct current circuit to an alternating current circuit. The electric translating apparatus is of the type commonly referred to as a parallel inverter. The translating apparatus includes a pair of electric valves each having an anode and a cathode and each of which comprises an arc discharge path including an ionizable medium at a pressure under operating conditions sufficient to support an arc-like discharge. The conductivity of the electric valves is controlled by magnetic means which establish magnetic fields transverse to the electron paths or transverse to the arc discharge paths. The magnetic control means comprises a core member and two windings, one of the windings being energized with a direct current to establish a substantially constant unidirectional magnetic field and the other winding is energized with alternating current to superimpose an alternating magnetic field upon the unidirectional field. The time of starting of the arc discharge is controlled by the composite effect of the unidirectional and the alternating components of the magnetic field. In order to control the time of starting of the arc discharges in the electric valves in accordance with the load transmitted by the translating apparatus, I provide a circuit for controlling the phase of the alternating component of magnetic field with respect to the anode-cathode voltage of the electric valves. This may be accomplished by means of a suitable phase shifting circuit such as a static impedance phase shifting circuit which is controlled in accordance with the current of the alternating current circuit or in accordance with the current of the direct current circuit.

In another of the illustrated embodiments of my invention, I provide an improved electric valve inverter circuit in which the electric valves are magnetically controlled. The alternating component of flux which renders the electric valves conductive at the desired times is obtained from a circuit including the aforementioned alternating current windings and a commutating capacitance. I also provide time delay means to maintain the electric valves non-conductive until the cathodes have been afforded ample time to assume a safe operating temperature. accomplished by employing a time delay relay which is energized from the direct current circuit and which is arranged to connect initially the commutating capacitance and the alternating current windings in a manner to prevent starting of the circuit and which is also arranged to assume a second position after the expiration of a predetermined interval of time to initiate operation of the circuit by connecting the alternating current windings and the capacitance in series relation across the anodes of the electric valves.

This is For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing.

Fig. 1 of the accompanying drawing diagrammatically illustrates an embodiment of my invention as applied to an electric valve translating circuit in which the electric valves are of the magnetically controlled type and in which the valves are controlled in accordance with the load transmitted by the translating apparatus. Figs. 2 and 3 represent certain operating characteristics of the embodiment shown in Fig. 1. Fig. 4 represents diagrammatically another embodiment of my invention in which protective means is provided and in which the alternating magnetic fields which control electric valves are obtained by utilizing the charging and discharging currents of the commutating capacitance.

In Fig. 1 of the accompanying drawing, there is diagrammatically illustrated an embodiment of my invention as applied to an electric valve translating circuit for transmitting power from a. direct current circuit I to an alternating current circuit 2 through electric translating apparatus including a transformer 3 and a pair of electric valves 4 and 5. The transformer 3 may comprise a primary winding 6 having terminal connections I and 8 and an electrically intermediate connection 9. Transformer 3 may also comprise a secondary winding I which is connected to the alternating current circuit 2. An inductance II may be connected in series relation with the direct current circuit I to smooth the fiow of current from the circuit I to the translating apparatus. To control the operation of the translating apparatus, I may employ a switch I2 which is also connected in series relation with the translating apparatus and the direct current circuit I.

Electric valves 4 and 5 each comprise an anode I3, a cathode I4 and may include a control member or grid I5 which is connected to the cathode I4. Electric valves 4 and 5 are of the type which employ an ionizable medium such as a gas at a pressure under operating conditions sufficient to support an arc-like discharge between the cathodes I4 and the anodes I3.

In order to control the conductivity of the electric valves 4 and 5, that is, to control the time during the half-cycles of anode-cathode voltage at which the electric valves are rendered conductive, I employ magnetic control means I6 and I! which are associated with electric valves 4 and 5 respectively. The magnetic control means I6 and I! each comprises a magnetic core member I8 having legs I9 and 20 which conjointly act as a magnetic path for the transmission of the flux of a magnetic field which intercepts the direction of the discharge of the associated electric valve. As a means for establishing a unidirectional magnetic field which tends to maintain the electric valves 4 and 5 nonconductive, I employ a circuit including windings 2I and 22 which are associated with electric valves 4 and 5 respectively. The windings 2I and 22 may be energized from any suitable source of direct current and in the arrangement of Fig. 1 are shown as being energized from the direct current circuit I through an adjustable resistance 23 which controls the magnitude of the direct current transmitted to windings 2I and 22 and hence serves to control the magnitude of the unidirectional component of magnetic field which is established transverse to the path of the discharges of electric valves 4 and 5.

To provide an agency for controlling the time of initiation of an arc discharge within electric valves 4 and 5 in accordance with the load transmitted by the translating apparatus, I provide windings 24 and 25 which establish alternating components of magnetic fields which are superimposed upon the unidirectional components of the magnetic fields and which vary in phase in response to the load transmitted by the translating apparatus. Windings 24 and 25 are, of course, associated with the proper portions of core members I8 of the magnetic control means It and II respectively.

As an agency for controlling the phase of the alternating current transmitted to windings 24 and 25 and hence to control the phase of the alternating components of fiux in accordance with the load transmitted by the translating apparatus, I provide a phase shifting circuit 26 which may be any one of the conventional types well known in the art. For the purpose of illustration, I have chosen to employ a circuit of the static impedance type including a transformer 27 which is energized from a suitable source of alternating current and in the arrangement shown is connected to be energized from the alternating current circuit 2 through a rotary phase shifting device 28. The transformer 21 comprises a secondary winding 29 having terminal connections and an electrically intermediate connection 30. Circuit 26 also includes phase shifting elements which comprise a resistance 3| and a saturable inductive reactance 32 comprising variable incluctance windings 33 and a control winding 34. A capacitance 35 may be connected. in series relation with the windings 33 to afford an additional phase displacement of the output voltage of the phase shifting circuit. The output voltage of the phase shifting circuit is obtained by way of a transformer 36. This output voltage, of course, varies in phase with respect to the voltage of the alternating current circuit 2. A capacitance 31 may be connected across the transformer 35 to compensate for the magnetizing current required by the transformer. A control circuit 38 is provided to control the phase of the output voltage of the phase shifting circuit 26 in accordance with the load transmitted by the translating apparatus. The control circuit 38 comprises any suitable means such as a current transformer 39 which is responsive to the load transmitted by the translating apparatus and includes a unidirectional conducting device such as an electric valve 40 which is arranged to transmit variable amounts of unidirectional current to the control winding 34 of the saturable inductance 32. While I have shown the control circuit 38 as being energized in response to the current circuit 2, it is to be understood that the circuit 38 may be energized in accordance with the current of circuit I or in accordance with any other electrical condition of the translating apparatus which varies in response to the load transmitted thereby. A commutating capacitance 4I may be connected across the anodes of the electric valves 4 and 5 to transfer or commutate the current between the electric valves 4 and 5.

The operation of the embodiment of my invention diagrammatically illustrated in the drawing will be explained by considering the system when power is being transmitted from the direct current circuit I to the alternating current circuit 2 through the electric valves 4 and 5 and the transformer 3. As is well understood by those skilled in the art, the electric valves 4 and 5 conduct current alternatingly so that there is established in the transformer windings 6 and iii an alternating flux. The capacitance 41 is effective to commutate the current between the electric valves. Furthermore, as is well understood by those skilled in the art, it is necessary that the electric valves 4 and 5 conduct current so that the current flows in winding 6 in a direction opposite to the C. E. M. F. In other words. the electric valves 4 and 5 are rendered conductive'within the region lying between the electrical degree lagging position and some angle slightly less than the electrical degree lagging position. In inverter operation, the maximum output of the inverter is obtained when the electric valves are rendered conductive at substantially the 180 electrical degree lagging position. As the time at which the electric valve is advanced during the positive half-cycle of applied anode-cathode voltage from the 180 electrical degree lagging position, the commutating voltage applied to the electric valve is increased. Since it is desirable to increase the commutating voltage as the load increases, I have found that I may accomplish this effect by advancing the phase of the alternating component of the magnetic field as the load increases.

Reference may be had to Fig. 2 of the drawing to explain the manner in which the electric valves 4 and 5 are rendered conductive by the composite effect of the unidirectional and the alternating components of the magnetic field. Curve a of Fig. 2 represents a half-cycle of anode-cathode voltage of one of the electric valves and curve b represents the magnetomotive force applied to the arc-paths of valves 4 and 5 by the current flowing in coils 24 and 25 respectively, and this curve is plotted with gauss as an ordinate and degrees as abscissa. Curve b may be considered as representing the alternating current control flux. Curve 0 is also plotted with gauss as an ordinate and degrees as abscissa and represents the critical or breakdown flux necessary to restrain the arc or glow from being initiated. It will be noted that curve 0 comprises two similar configurations above and below the zero axis, the upper half of the curve representing the critical or breakdown flux for magneto-motive force in one direction and the lower half of the curve representing the same conditions when the magnetomotive force is in the opposite direction. It is apparent that when the flux caused to move through the core i8 is greater than the flux values represented by the upper half of the curve 0, for a given direction of direct flux or greater than the values represented by the lower half of the curve 0 for the opposite di rection of the direct flux, the are or glow will be restrained so long as the flux in the core remains greater than the amount set forth. On the other hand, if the flux in the core is less than the values indicated by either half of the curve 0, depending upon the direction in which the direct flux is moving, the are or glow'will be initiated and will 'continue to fiow throughout the remainder of the positive half cycle of anode voltage. Consequently, whenever the curve b which represents the alternating control flux introduced by the coils 24 and 25, intercepts either half of the curvec, the are or glow will be initiated since the alternating control flux becomes less at times than the amount of flux necessary to restrain the are or glow from starting.

The phase shifting circuit 26 controls the phase of the alternating component of fiuX for each valve as represented by the curve I) to control the phase of this component relative to the anode-cathode voltage to render the electric valves conductive at different times during the cycle depending upon the load condition imposed on the translating apparatus. For example, in Fig. 3, the line 01 represents the unidirectional components of the magnetic field produced by windings 2i and 22. For the particular values indicated by the curves of Fig. 3, one of the electric valves, as, for example, electric valve 4, will be rendered conducting at the time e. If the load transmitted by the translating apparatus is increased, the output voltage of the circuit 26 will be advanced in phase to advance the position of the curve b to the position b rendering the electric valve 4 conductive at point e. Conversely, if the load decreases, the phase of the output voltage of circuit 25 will be retarded effecting retardation in the phase of the alternating component of the magnetic field. In this manner the commutating voltage of the inverter is controlled in accordance with the load transmitted by the apparatus. The shifting in phase of the alternating component of the magnetic field is a very satisfactory arrangement for precisely controlling the conductivity of the electric valves in circuits of this nature.

In Fig. 4 of the accompanying drawing, there is diagrammatically illustrated another embodiment of my invention which is similar in many respects to that shown in Fig. l and corresponding elements have been assigned like reference numerals. I provide in connection with a circuit of this nature, commonly referred to as a parallel inverter circuit, means for starting the inverter and an improved arrangement for supplying the alternating component of the magnetic fields which control the conductivities of the electric valves 4 and 5. In the arrangement of Fig. 4, the commutating capacitance 41 is connected in series relation with the windings 24 and 25 so that the charging current of the capacitance 41 supplies the energization for windings 24 and 25.

As a protective agency for the electric valves 4 and 5 whereby there is afforded a sufiicient interval of time for the cathodes l4 to assume safe operating temperatures, I employ a time delay means 42 which comprises an armature member 43, a movable contact 44 and sets of sta tionary contacts 45 and 46. The time delay means 42 also includes actuating coils 4! and 43, the coil 48 being associated with a magnetic core member 49 which is of a material such as an iron, nickel and copper alloy, the permeability of which decreases as its temperature increases. The time delay means 42 is energized from the direct current circuit I and is arranged to maintain the armature member 43 in the position shown for a predetermined interval of time after the closure of switch l2. After the expiration of the interval of time, the magnetic effect of the coil 48 and the core member 49 becomes much smaller due to the decrease in the permeability of the core 4t, permitting the coil 47 to move the armature member 4-3 to a position in which movable contact 44 engages stationary contacts 45. A current limiting resistance 50 may be employed limit the charging current which flows through the capacitance 4| and windings 24 and 25 during the initial preheating period. Cathodes E4 of electric valves 4 and 5 are connected to be energized from the direct current circuit I, and the magnitude of the current transmitted thereto may be controlled by employing a serially connected resistance 5| of suitable value.

The embodiment of my invention shown in 4 operates in substantially the same manner as that explained above in connection with Fig. 1. That is, the translating system, after the initial heating period, transmits energy from the direct current circuit to the alternating current circuit 2 through transformer 3 and electric valves 4 and 5. The electric valves 4 and 5 are rendered conductive by the composite effect of the unidirectional and the alternating components of the magnetic fields produced by the magnetic control means l6 and I1 respectively. Due to the fact that the capacitance 4| is alternately charged to different polarities, the current transmitted through windings 24 and 25 will be alternating to provide the alternating components of field which, acting against the unidirectional components, renders the valves conductive at the desired times.

The time delay means 42 operates to assure that the cathodes |4 attain a sufficiently high or safe operating temperature after the closure of the switch |2. Upon the closure of the switch I2, the cathodes l4 and the coils 41 and 48 of the time delay means 42 are simultaneously energized. Initially the magnetic pull of the coil 48 predominates over that produced by coil 41 so that the serially connected capacitance 4| and the windings 24 and 25 are connected between the anode |3 of electric valve 5 and the negative terminal of the direct current circuit I through contacts 46 and resistance 50.

When the capacitance 4| and the windings Z4 and 25 are so connected, the capacitance 4| will be charged from the circuit I so that the righthand plate is positive, but due to the fact that the charging current decreases after the initial charge, there is no alternating component of flux to co-act with the unidirectional component or field so that the electric valves 4 and 5 are maintained non-conductive by the unidirectional component.

After the expiration of a predetermined interval of time established by the design of the time delay means 42, the permeability of the core member 49 decreases and the coil 41 moves the movable contact 44 into engagement with contacts 45. Under this latter condition the serial connected capacitance 4| and the windings 24 and 25 are connected across the anodes l3 of electric valves 4 and 5, placing the valve circuit in condition for operation. When the movable contact 44 engages at the stationary contacts 45, the capacitance 4| discharges causing current to flow through windings 24 and 25 of a magnitude and direction which renders electric valve 5 conductive. The electric valves 4 and 5 are rendered conductive alternately by the alternating current transmitted through the windings 24 and 25, and the electric valves are rendered non-conductive by the commutating capacitance 4|.

While I have shown and described my inven tion as applied to a particular system of connections and as embodying various devices diagrammatically shown, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, an alternating current circuit, a load circuit, electric translating apparatus connected between said circuits and including an electric discharge device comprising an anode, a cathode and an ionizable medium at a pressure under operating conditions sufiicient to support an arc-like discharge, and means for controlling the conductivity of said electric discharge device comprising a circuit for producing a unidirectional magnetic field which intercepts the direction of said discharge and a circuit responsive to an electrical condition of one of said first mentioned circuits for superimposing on said unidirectional field an alternating component of flux which is variable in phase with respect to the anode-cathode voltage of said electric discharge device to control the time during cycles of anode-cathode voltage at which said discharge device is rendered conductive.

2. In combination, an alternating current circuit, a load circuit, electric translating apparatus connected between said circuits and including an electric discharge device comprising an anode, a cathode and an ionizable medium at a pressure under operating conditions sufficient to support an arc-like discharge, means for producing a unidirectional magnetic field which intercepts the direction of said discharge, means for superimposing an alternating component of flux on said unidirectional field, and means responsive to the current transmitted by one of said first mentioned circuits for controlling the phase of said alternating component of flux relative to the anode-cathode voltage of said electric discharge device to control the time during cycles of anode-cathode voltage at which said discharge device is rendered conductive.

3. In combination, an alternating current circuit, a direct current circuit, electric translating apparatus connected between said circuits and comprising an inductive winding having terminal connections and a connection electrically intermediate the terminal connections and a pair of electric discharge devices each having an anode, a cathode and an ionizable medium at a pressure under operating conditions sufiicient to support an arc-like discharge, said terminal connections being connected to the anodes of said discharge devices and said direct current circuit being connected to the intermediate connection and the cathodes of said discharge device, individual means for producing unidirectional magnetic fields which intercept the direction of said discharges, windings for superimposing alternating components of flux on said unidirectional fields to control the time during cycles of anodecathode voltage at which said discharge devices are rendered conductive, a capacitance connected in series relation with said windings, and time delay means connected to be energized from said direct current circuit to delay the initiation of arc discharges in the electric discharge devices for a predetermined time after the energization of said cathodes and comprising means for connecting the serially connected windings and capacitance initially between the anode of one of said discharge devices and the negative terminal of said direct current circuit and for subsequently connecting the windings and commutating capacitance in series relation across the anodes.

4. In combination, an alternating current circuit, a direct current circuit, electric translating (6 apparatus interposed between said circuits and comprising an inductive winding having terminal connections and a connection electrically intermediate said terminal connections and a pair of electric discharge devices each comprising an anode, a cathode and an ionizable medium at a pressure under operating conditions sufiicient to support an arc-like discharge, said terminal connections being connected to the anodes of said discharge devices and said direct current circuit being connected to the intermediate connection and the cathodes of said discharge devices, a pair of core members each associated with a difierent one of said electric discharge devices, a circuit energized from said direct current circuit and associated with said core members for establishing unidirectional magnetic fields which intercept the direction of said discharges, a commutating capacitance for effecting transfer of current between said pair of electric discharge devices, and a circuit associated with said core members and connected in series relation with said oommutating capacitance for producing alternating components of flux which are superimposed upon said unidirectional fields to control the time during cycles of anode-cathode voltage at which said discharge devices are rendered conductive. 

